security-manager-tests: fix security_manager_48_groups_get

security-manager-tests: fix security_manager_48_groups_get

This test case is verifying whether security_manager_groups_get() returns
proper array of groups currently mapped to any of known privileges.

The test case expected the function only to return groups explicitly added
by security-tests. But now this feature is actively used on the image. There
are groups mapped to privileges, that are not setup by security-tests, but
are part of the system security policy.

Fix the test case by reading mapping from
/usr/share/security-manager/policy/privilege-group.list.
The groups configured in that file are now also expected.

Change-Id: I01ccc45a773b774144ab7f04f7c48bb2192c5ce1